1. Field of the Invention
The present invention relates to a method for correcting a recording head, and a recording head corrected by use of the correction apparatus, and also relates to a recording apparatus using such recording head. More particularly, the invention relates to a correcting method of the recording head, for correcting driving for a specific number of recording elements, for example. The invention also relates to an apparatus therefor, and a recording head corrected by use of such apparatus, and a recording apparatus using such head as well.
2. Related Background Art
A printing apparatus, or the printer unit provided for a copying machine, a facsimile equipment or the like is structured to record images each formed by dot patterns on a recording medium such as a paper sheet, a thin plastic plate or a cloth, in accordance with image information.
Of such printing apparatuses, a particular attention is given to a printing apparatus that mounts thereon a recording head of ink jet type, thermal type, LED type or the like as a low-cost apparatus. Such apparatus is usually structured with a plurality of printing elements, arranged on a substrate, corresponding to a number of dots to be printed.
In a recording head having the printing elements (recording elements) arranged corresponding to a printing width, since the printing elements are constituted in the same processes as those of the semiconductor manufacture, there has been a tendency in recent years that the conventional mode in which the driving integrated circuit is produced as a separate device is being developed into a mode in which the driving circuit is incorporated as one structure on the same substrate having printing elements arranged thereon. As a result, a structure of the circuit for driving the recording head is prevented from being complicated, and the printing apparatus is made smaller accordingly, thus attaining the significant reduction of manufacture costs.
Particularly, the ink jet recording method is of the type that thermal energy is applied to ink to generate bubbles and discharge the ink by pressure of the bubbles, and it has an excellent responsability to recording signals. This method also has an advantage that the discharge ports can be arranged in higher density. As compared with other recording methods, therefore, the ink jet recording method is remarkable very much.
In a case where a recording head is manufactured by utilizing the semiconductor manufacturing techniques, it is extremely difficult to produce all the printing elements without defects particularly in arrangement of a number of printing elements all over the surface of a substrate in order to cover a recording width. As a result, the production yield of recording heads is poor in the manufacture processes, hence making the costs higher inevitably. In some case, then, the manufacture of the head cannot be realized from the viewpoint of the manufacturing costs.
In this respect, therefore, there has been proposed a method for obtaining an elongated recording head that meets a required recording width by providing a plurality of recording heads whose production yield is higher, such as those provided with the printing elements each having a comparatively smaller number of ink discharge ports of 32, 48, 64, or 128 to be arranged in high precision on a substrate (or top and bottom thereof) in accordance with the density of arrangement of the printing elements as needed. A method of the kind is disclosed, for example, in Japanese Patent Application Laid-Open Nos. 55-132253, 2-2009, 4-229278, 4-232749, 5-24192, and the specification of U.S. Pat. No. 5,016,023, and among some others.
In recent years, it has become easier to manufacture a full-line recording head by arranging the printing devices, each having comparatively small numbers of ink discharge ports, such as 64 or 128, on a substrate, and then, aligning/adhering such substrate (hereinafter referred to as a printing component) in plural numbers on a base plate in good precision, in correspondence to the recording width as needed.
Here, however, although it has become easier to manufacture the full-line recording heads in this manner, there are still problems as hereinbelow.
For example, unevenness in the performances of printing components (substrates) thus arranged, unevenness in the performances of the printing elements in the vicinity of each gap between the printing components, and degradation of image quality caused by difference in density due to heat accumulation or the like per driving block for recording.
Particularly, in the case of the recording head of ink jet recording type, the production yield in its manufacture processes tends to be lowered not only by the problem of the variation between the printing elements in the vicinity of each gap between the printing components as arranged, but also, the problem of the ink fluidity that may be lowered by the presence of gaps between the printing components. Therefore, despite the high performance of a recording head of the kind the fact is that such recording head has not been promoted on the market.
Also, there is means for correcting the density unevenness of the recording head, such as a method disclosed in Japanese Patent Application Laid-Open No. 6-34558 wherein the density unevenness is corrected by measuring dot diameters. However, there is still a room for improvement as to the reproducibility of recorded dots. For example, when a one-line recording is executed, fine changes are noticed in the characteristics of recorded dots in the next line or several tens or several hundreds of lines later (which is termed as the fluctuation per recorded dot). Here, since a specific event (dot diameter) that includes this fluctuation is regarded as the data on the density unevenness, it is impossible to obtain a satisfying result with the execution of only one time of correction. In order to obtain a desired image, there is a need for obtaining the data on recorded dots several times for such correction. Further, when electric energy is to be converted into thermal energy in accordance with such correction data, the energy which is larger than a usual value is applied to the printing elements for low density. As a result, there is the failure in reliability regarding the durability of the recording head.
Further, in the estimation method using OD values, which is one of the conventional methods for correcting density unevenness, or the method of obtaining the correction data by estimating density unevenness from the variation of data on the dot diameters obtained in the manufacture processes of the recording head, there are the cases where the density unevenness is not corrected exactly, because there is not necessarily a good correlationship between the performance of a recording head.
The present invention is invented by taking into consideration the problems in the conventional apparatuses/methods as discussed above.
It is an object of the invention to provide a recording head which can be manufactured with a high production yield at lower costs by the execution of density unevenness correction reliably without giving any particular load to the recording head, and to provide a recording apparatus that uses such head as well.
It is another object of the invention to provide a method for correcting the head described above, and a correction apparatus therefor.
In order to achieve these objects, there is provided a method for correcting a recording head provided with a plurality of recording elements and memory means capable of storing data, comprises the steps of recording preliminarily recording patterns on a recording medium by use of the recording head in accordance with plural kinds of signals applied thereto; selecting one of the plural kinds of signals, for a predetermined unit of said recording elements, from the density distributions of the image pattern recorded on the recording medium so as to make the density of the recorded image equal to the reference density or the approximate value thereof; preparing as the correction data data for selecting one of the plural kinds of signals for a predetermined unit of the recording elements and storing the correction data on the memory means of the recording head as the initial correction data; and selecting either one of the initial correction data and the correction data output by the correction data controlling unit for generating arbitrary correction data for a predetermined unit of said recording elements and transmitting data to the recording head in accordance with the selected data.
The above-mentioned recording head is arranged to prepare the correction data stored on the memory means as the initial correction data fundamentally for correcting the density unevenness. A recording apparatus which mounts the recording head thereon is arranged to comprise a correction data controlling unit that generates arbitrary correction data, and transmission means for selecting one of the correction data output from the correction data controlling unit and the initial correction data to transmit to the recording head.
Also, in accordance with another aspect of the present invention, there is provided a method characterized by preparing correction data generating means that generates the correction data for the recording elements for a predetermined unit with reference to the image data corresponding to one line of the recording elements from the m-th line (m=log2 n) to the line immediately before, and selecting appropriately one of the correction data output by the correction data controlling unit for generating arbitrary correction data and the initial correction data.
With the structure described above, the present invention makes it possible to provide prints of higher quality without density unevenness, because the density unevenness correction data are stored as the initial correction data on the memory in the recording head and it is possible to select one of the initial correction data and the arbitrary correction data which are generated with reference to the image data or the like.
Also, in accordance with said another aspect of the present invention, it is possible to provide prints of higher quality without density unevenness by appropriately selecting one of the initial correction data and the correction data generated with reference to the image data corresponding to one line of the recording devices from the m-th line (m=log2 n) to the line immediately before.